Added additional invalidations for fixed background-attachments.

Fixed background attachments must be invalidated when they are moved, since 
the background will change. If these are on their own layers, they must be 
invalidated when any ancestor is scrolled.


R=vollick@chromium.org
BUG=282226

Review URL: https://codereview.chromium.org/276473004

git-svn-id: svn://svn.chromium.org/blink/trunk@173972 bbb929c8-8fbe-4397-9dbb-9b2b20218538